The objective of this work was to evaluate the behavior of six cotton cultivars (BRS-Ipê, BRS-Aroeira, BRS-Cedro, Fibermax 966, DeltaOpal and CNPA Ita 90-II) in relation to Rhizoctonia solani AG-4 and the benefits of cotton seed treatment with fungicides, for each tested cultivar, for the control of damping-off in relation to inoculum densities of this fungus. This experiment was carried out at greenhouse conditions at Embrapa Agropecuária Oeste, in Dourados, MS. Four inoculum densities were tested (0; 1; 2 and 3g of fungus inoculum/plastic tray with dimensions of 56x35x10cm) in the trial. The evaluations were done based on symptoms development and seedling survival, using initial and final emergence and pre and pos damping-off data. Treated and untreated seeds with fungicides mixture tolylfluanid + pencycuron + triadimenol (30+50+50g a.i./100kg of seeds) were sowed in sand contained in plastic trays, by placing in equidistant 3-cm-deep wells. The inoculation with R. solani AG-4 was done by the homogeneous distribution of the fungus inoculum onto the substrate. The fungus was grown for 35 days on autoclaved oat seeds and then ground to powder using a mill (1mm). Significant effect of the interactions cultivars x inoculum densities, cultivars x fungicides and inoculum densities x fungicides were oberved. The cultivars behavior was significantly influenced by different populations of R. solani. Results showed that the higher the inoculum density, the higher the disease level and the lower the emergence rates. It was also demonstrated the importance of cotton seed treatment with fungicides, with best results in relation to emergence and disease level (damping-off and lesioned seedlings), regardless of tested cultivar, being obtained when the seeds were treated with tolylfluanid + pencycuron + triadimenol. It was still observed that pathogen population significantly influenced the benefits of seed treatment, since the performance of fungicides was better when inoculum densities were low. In the absence of seed treatment with fungicides, differences among the cultivars in relation to R. solani were observed, being distinct in CNPA ITA 90 II and BRS Aroeira, followed by BRS Cedro and BRS Ipê, which showed higher tolerance to R. solani.
damping-off; emergence; inoculum level; Gossypium hirsutum
